Method and apparatus for the collection of near real time confirmation samples

Abstract

A system for the collection of near real time confirmation samples is provided to quickly eliminate false positive alarms by confirming the presence or absence of a chemical agent when a monitor operating in near real time to detect the presence of that chemical agent generates an alarm. The confirmation sampling system is synchronized with the near real time monitor and the confirmation sampler and monitor draw common samples of the atmosphere of concern. In the event that the monitor generates an alarm, the confirmation sampler preserves the sample taken contemporaneously with the alarm event for separate analysis, and also takes and preserves one or more follow-on samples.

We claim:  
     
       1. A method for confirming the presence or absence of a particular chemical compound upon the report thereof generated by an analytical system that is arranged to detect the presence of that chemical compound in the gas being monitored, said method comprising: 
       providing a monitoring system that cyclically samples a gaseous atmosphere to obtain a sample for analysis and immediately thereafter analyzes said sample to determine the presence or absence of said chemical compound;  
       providing a confirmation sampler, said confirmation sampler having at least two sorbent-containing sampling tubes that are arranged such that one sampling tube is sampling the same gaseous atmosphere as is said monitoring system while the other sampling tube is purging to desorb contaminants captured on said sorbent;  
       providing control means that synchronize the operation of said confirmation sampler with that of said monitoring system, so that when the monitoring system is sampling so also is one of the tubes of the confirmation sampler; and  
       causing said monitoring system to generate an alarm signal upon detection of said chemical agent, said signal also causing the confirmation sampler to retain and not desorb the sampling tube collected during that cycle of the monitoring system which triggered said alarm to thereby leave the sample collected by said sampling tube available for retrieval and analysis for confirmation of the presence or absence of said chemical agent.  
     
     
       2. The method of  claim 1  wherein said chemical compound is a toxic chemical agent. 
     
     
       3. The method of  claim 1  wherein said monitoring system is a near-real-time monitor, and is arranged to detect sub time weighted average concentrations of said agent. 
     
     
       4. The method of  claim 1  wherein said monitoring system is arranged to draw a gas sample through a sorbent-packed sample tube for a pre-determined time, and then to desorb said tube into an analyzer. 
     
     
       5. The method of  claim 4  wherein said analyzer is a gas chromatograph. 
     
     
       6. The method of  claim 4  wherein said analyzer is a mass spectrometer. 
     
     
       7. The method of  claim 1  wherein said control means that synchronizes operation of said confirmation sampler with that of said monitoring system does so by generating a timing signal that is transmitted to said sampler at the beginning of a monitoring system cycle. 
     
     
       8. The method of  claim 1  wherein said sampling tubes are DAAMS tubes. 
     
     
       9. The method of  claim 1  wherein said confirmation sampler collects a second sample on said second sampling tube after receiving an alarm signal from said monitoring system, and preserves said second sample for retrieval and analysis. 
     
     
       10. A system for the monitoring of a gaseous atmosphere to detect a particular chemical compound in said atmosphere and to confirm the presence or absence of that compound, said system comprising: 
       a monitor and alarm system that is arranged to cyclically and continuously monitor said gaseous atmosphere by drawing a sample from said gaseous atmosphere and to immediately thereafter analyze said sample to detect and to report the presence of said compound;  
       a confirmation sampler, said confirmation sampler having at least two sorbent-containing sampling tubes;  
       means for drawing a gaseous sample alternately through the first of said sampling tubes and then through the second of said sampling tubes;  
       means for purging contaminants sorbed on packing contained in said sampling tubes after said gaseous sample has been drawn through the tubes;  
       means to synchronize the cyclic operation of said monitor and said confirmation sampler so that during that time interval during which the monitor is sampling, so also is one of said tubes of the confirmation sampler;  
       means responsive to a report of said chemical compound generated by the monitor, said responsive means arranged to cause said confirmation sampler to retain and not to purge that sampling tube employed during the cycle of said monitor that generated said report.  
     
     
       11. The system of  claim 10  wherein said monitoring and alarm system includes means to draw said sample of gaseous atmosphere through a sorbent-packed sample tube for a pre-determined time, and to then desorb said tube into an analyzer. 
     
     
       12. The system of  claim 11  wherein said analyzer is either a gas chromatograph or a mass spectrograph. 
     
     
       13. The system of  claim 10  wherein said confirmation sampler includes a first and a second four-port, two-position valve arranged in communication with said sampling tubes so that when said valves are in a first position, gas being sampled is routed through the first of said sampling tubes and a heated purge gas is routed through the second of said sampling tubes. 
     
     
       14. The system of  claim 13  wherein said valves, when in a second position, route the gas being sampled through the second of said sampling tubes and route a heated purge gas through the first of said sampling tubes. 
     
     
       15. The system of  claim 10  wherein said means for drawing a gaseous sample through said sampling tubes includes a vacuum pump and means to measure and control the flow of gas through said tubes. 
     
     
       16. The system of  claim 10  wherein said means for purging contaminants sorbed on packing contained in said sampling tubes comprises means for flowing a heated stream of purge gas through said sampling tubes in a direction opposite to the direction of gas flow during sampling. 
     
     
       17. The system of  claim 10  wherein said sampling tubes are DAAMS tubes. 
     
     
       18. The system of  claim 10  wherein said confirmation sampler includes a four-port, two-position valve and four check valves arranged in association with said sampling tubes to direct flow of the gas being sampled through a first one of said sampling tubes and then to exhaust and to direct a stream of hot purge gas through the second one of said sampling tubes and then to exhaust when said two-position valve is in a first position, and to direct a stream of hot purge gas through the first of said sampling tubes and then to exhaust, and to direct flow of the gas being sampled through the second one of said sampling tubes and then to exhaust when said two-position valve is in its second position. 
     
     
       19. The system of  claim 18  including a two-port, two-position valve arranged to control the flow of purge gas from a purge gas source to said four-port valve. 
     
     
       20. The system of  claim 10  wherein said means to synchronize the cyclic operation of said monitor and said confirmation sampler includes means to generate a timing signal that is transmitted to said sampler at the beginning of a monitor cycle.